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From the den of the Artful Bodger, a poor man's DRO!

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John Hill:

The poor mans DRO!  Mounted on a 'lecturn' fixed to the back of the lathe carriage.


How the cables are attached to the back of the DROs, it is a slip joint which is necessary as the carriage travel is more than the maximum length of these DROs,  it just hits the end and the cable slips.


How it looks behind the DROs.



One of the cable anchors.



One end of the cross slide cable loops under the lathe bed.


The DROs cost about 50 quid and the cables another 10 or so including the length of stainless fishing trace I had to use for the longer cable.

So how good is it?  Wellll I guess you get what you pay for and this is not a 500 quid DRO set but it is certainly functional and I can wind the carriage back and forth then return to a marked spot and it reads zero. There is a slight backlash which I can probably work on, the cross slide is worse than the carriage travel as far as back lash is concerned  which may be because that cable is spring tensioned, the long cable is tensioned by screw adjuster and has less backlash.  I still need to dress the flexible sections and shorten where I can as I believe the flexible sections are the cause of the backlash, but I am not going to get too obsessive about this.

All in all I am really pleased with the result, it did not cost much and the DROs are well out of the way of coolant etc, plus the steel lecturn gives me a place to places notes and small drawings etc.

SPiN Racing:
WOW... very inventive way to get the DRO setup taken care of!!

I would imagine once you get used to the slight backlash in the cables.. its easy to be accurate.

bogstandard:
John,

Very inventive, but your choice of using bowden cables is the downfall.

No matter what you do, you will never get them to have zero backlash unless it it a perfectly straight setup, and how you have done it, tensioned with some sort of spring. The problem is the running clearance between the cable and the outer sheath, and going around corners, you will always get some flexing of the outer sheath.

The method was used many years ago in the beginnings of DRO's on model engineering equipment, but without the outer cable. It operated similar to a steel tape measure, where the amount of cable pulled out, turned a rotary encoder. It did have the advantage that it could be used with a rotary table as well, as the cable just wrapped around the turny bit on top.

I don't know if anyone actually bought any, as they soon disappeared from the market.

I wish you luck on your efforts to get zero backlash.


John

Kludge:
Bogs, as I was reading your message, the first thing that came to mind was to use hydraulics instead.  A cylinder at each end and a well purged system would do nicely, though it might be a bit upset at any overrun at either end.  Gotta think about that bit.  It could be fun, though.  :)

Best regards,

Kludge

bogstandard:
Absolutely great Kludge, until you have a saddle feed like mine, of 3ft. I wouldn't like to be on the other end of a syringe that long. :lol:

Bogs

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